Neurological stimulators have been developed to treat pain, movement disorders, functional disorders, spasticity, cancer, cardiac disorders, and various other medical conditions. Implantable neurological stimulation systems generally have an implantable signal generator (sometimes referred to as an “implantable pulse generator” or “IPG”) that is operably coupled to one or more leads that deliver electrical signals or pulses to neurological tissue or muscle tissue. For example, several neurological stimulation systems for spinal cord stimulation (SCS) have cylindrical leads that include a lead body with a circular cross-sectional shape and multiple conductive rings spaced apart from each other at the distal end of the lead body. The conductive rings operate as individual electrodes or contacts to deliver electrical signals to the patient. The SCS leads are typically implanted either surgically or percutaneously through a needle inserted into the epidural space, often with the assistance of a stylet.
Once implanted, the signal generator applies electrical signals to the electrodes, which in turn modify the function of the patient's nervous system, such as by altering the patient's responsiveness to sensory stimuli and/or altering the patient's motor-circuit output. In particular, the electrical signals can generate sensations that mask or otherwise alter the patient's sensation of pain. For example, in many cases, patients report a tingling or paresthesia that is perceived as more pleasant and/or less uncomfortable than the underlying pain sensation. In other cases, the patients can report pain relief without paresthesia or other sensations. As used herein, unless explicitly stated otherwise, the terms “pulses” and “signals” are used interchangeably to include any waveform shapes, whether continuous or discontinuous, including but not limited to sinusoidal or non-sinusoidal waves such as square waves, triangle waves, sawtooth waves, etc.
Implantable signal generators generally include a communication antenna that allows operational parameters of a stimulation system to be altered, without necessitating a hard-wired external connection. Additionally, implantable signal generators often include a charging coil that allows a battery in the implantable signal generator to be recharged from an external power source. The design of the communication antenna and the charging coil, and their locations within the implantable signal generator, can significantly impact the performance of the stimulation system. If the antenna and/or the coil are poorly positioned or shielded, updating operational parameters and/or charging the implantable signal generator can be difficult or impossible. For example, in many existing systems it can be difficult for a patient or an operator to correctly position an external device to transmit signals to the implantable signal generator. Additionally, poor coil design or shielding interference can decrease the efficiency of the charging process and cause increased heating. Metal shells or casings that implantable signal generators often include can at least partially contribute to the effects described above. Positioning the communication antenna and/or charging coil outside of the casing can often partially alleviate some of these concerns. However, externally positioned components can increase the complexity and costs associated with the manufacturing of a device. Prior systems suffer from many of these and/or additional drawbacks.